Aromatic polyimides have the highest level of heat resistance among polymers, also have excellent mechanical characteristics, electric characteristic, and other characteristics, and thus they are used as a material in a wide range of fields.
On the other hand, the aromatic polyimide has generally poor processability, and thus is unsuitable particularly for melt molding or as the matrix resin of fiber-reinforced composite materials. For that reason, imide oligomers whose terminals are modified with a thermal cross-linking group have been proposed. Among them, an imide oligomer whose terminals are modified with 4-(2-phenylethynyl)phthalic anhydride is well balanced in moldability, heat resistance, and physical characteristics, and is disclosed, for example, in Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, Non-Patent Document 1, and Non-Patent Document 2.
Patent Document 1 discloses a terminal-modified imide oligomer having a logarithmic viscosity of 0.05 to 1, which is obtained by reaction of 2,3,3′,4′-biphenyltetracarboxylic dianhydride having a bend, non-planar structure, an aromatic diamine, and 4-(2-phenylethynyl)phthalic anhydride; and a cured product thereof. Patent Document 1 also describes that the invention can provide a highly practical novel terminal-modified imide oligomer, and a novel cured product of the terminal-modified polyimide having high heat resistance and good mechanical characteristics such as elastic modulus, tensile strength, and elongation, as the advantageous effects.
Patent Document 2 discloses a terminal-modified imide oligomer having a low melt viscosity and moldable in resin transfer molding or resin injection molding, which is obtained, for example, by reaction of (a) a diamine bonded product obtained by bonding 50% by mole or more of a soft diamine such as 1,3-bis(3-aminophenoxy)benzene or 1,3-bis(4-aminophenoxy)benzene to a hard diamine such as 1,3-diaminobenzene, 9,9′-bis(4-aminophenyl)fluorene, or 3,4′-diaminodiphenyl ether, (b) an aromatic tetracarboxylic dianhydride such as 3,3′,4,4′-biphenyl tetracarboxylic dianhydride, 4,4′-oxydiphthalic anhydride, pyromellitic dianhydride, or 4,4′-biphenoxydiphthalic anhydride, and (c) an end-capping agent such as 4-phenylethynyl phthalic anhydride.
Patent Document 3 discloses a terminal-modified imide oligomer represented by following General Formula:
(wherein R1, R2, and R3 show an aromatic diamine residue, R1 is a divalent aromatic diamine residue derived from 9,9-bis(4-(4-aminophenoxy)phenyl)fluorene, p and q are q≥0 when R3═R1 and q≥1 when R3═R2, and they satisfy the relationships of p≥0, 1≤p+q≤20, and 0≤q/(p+q)≤1; and an arrangement of repeating units may be either a block or random.)
The present inventors have already found that an aromatic imide oligomer, which is synthesized from an aromatic diamine including 2-phenyl-4,4′-diaminodiphenyl ether and a starting material compound including 1,2,4,5-benzene tetracarboxylic acid, and is modified terminals of the resulting product with 4-(2-phenylethynyl)phthalic anhydride, shows excellent solvent solubility, melt flowability at a high temperature, and moldability, and a thermally cured product thereof exhibits excellent heat resistance and sufficient mechanical characteristics; and have disclosed in Patent Document 4.